Effects of LDX on Cognitive Processes and Appetite

We will investigate the effect of LDX on neural responses to food stimuli using fMRI, and if/how liking ratings modulate these responses. The participants will perform a food and non-food rating task in the scanner, to measure reward-responses. Participants will view a range (36 each category) of high -and low-calorie food (equally distributed in sweet and savoury), and non-food items (visually matched). All items will be scored for appealing/liking with the use of a button box, varying from 1 (not at all) to 5 (very much). Each item will be presented for 3000ms followed by a fixation cross (500 - 1500ms). (3 x 7 min = 21 min)

We will determine if LDX administration has an effect on appetite and mood ratings via a visual analogue scale (VAS) in a hungry and sated state. Participants will drag a cursor from 0cm (not at all) to 10cm (most I could imagine) to self-report mood and appetite.

We will determine if LDX modulates emotional processing. The ETB is a computerised battery that comprises the following tasks:

FERT: Faces will appear on a screen ranging in emotions. The participant is instructed to classify each expression as quickly and accurately as possible. Accuracy, response bias, reaction time, and target sensitivity.

ECAT: 60 positive and negative adjectives will be presented for the participant to indicate if they would like to be described as such. Accuracy and reaction times.

EREC: The participants will be asked to recall as many words from the ECAT as can be remembered within a 4-minute period. The number of correct words recalled and respective valence will be measured.

EMEM: Participants will be presented with personality descriptors derived from the ECAT, along with matching novel distractor words. Participants will indicate if the descriptor was presented before. Accuracy, reaction time, response bias, and target sensitivity.

We will investigate the effect of LDX on working memory. To assess working memory and working memory capacity, participants will complete a visuospatial n-back task. The participant is presented with a sequence of circles on a 3x3 grid. The participant is instructed to indicate whether the current circle location matches the location of the circle n trials earlier. In this design, participants will identify if the circle matches the circle 2 and 3 trials back on separate cycles. Participants will complete 70 trials of each n-back condition. This task takes approximately 10 minutes to complete.

We will investigate the effect of LDX on attention. This task is a series of white letters presented on a grey background in random order, modelled on the Conner's Continuous Performance Task. Participants are instructed to press the space bar for every letter except 'X'. Letters will be presented for 900ms. Accuracy and reaction time will be measured. The task duration is 14 minutes.

We will investigate LDX effect on cognitive control (ie inhibition). Participants will complete the delay-discounting task for money and food. The delay-discounting task measures the extent to which participants are willing to delay the receipt of a reward, in exchange for receiving a higher-value reward, and is generally considered to reflect impulsive behaviour. This task is a monetary discounting task with nine delays ranging from one day to one year. On a screen, participants see the question 'Which would you prefer?', with two choices: £xx now or £xx after a delay (varying from one day to one year), and will be asked to choose between the two. A similar paradigm will be used for food, with questions consisting of food variables instead of money. Questions will require a choice between a smaller amount of food now, and a larger amount later. Area under the curve will be calculated.

We will measure the effect of LDX on inhibition using the Stop Signal Task. The stop signal task requires the participant to identify the direction of a circle's location on the screen (i.e., left or right). If, however, the circle is encased in another circle, then the participant is to withhold a response. Successful inhibition, commission errors, and reaction time will be measured.

We will investigate the activation changes in brain regions associated with reward to food when viewing pictures of food.

When assessing changes in activation we will assess how activity in separate brain regions changes when attending to food pictures compared to when attending to visually-matched non-food pictures.

We will investigate the changes in functional connectivity between brain regions associated with reward to food when viewing pictures of food.

When looking at changes in functional connectivity we will assess how the relationship between activity in any two or more brain regions is altered when attending to food pictures compared to when attending to visually-matched non-food pictures.

We will investigate the effect of LDX on brain regions associated with cognitive control, during performance of a delay discounting task (Outcome 8). When assessing changes in activation we will assess how activity in separate brain regions changes when making decisions about food compared to when making decisions about money.

We will investigate the changes in functional connectivity between brain regions associated with cognitive control.

When looking at changes in functional connectivity we will assess how the relationship between activity in any two or more brain regions is altered when making decisions about food compared to when making decisions about money.